1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus each including the electrophotographic photosensitive member.
2. Description of the Related Art
An oscillation wavelength of semiconductor laser, which has been frequently used as an image exposing device of an electrophotographic photosensitive member is, at present, a long wavelength such as 650 to 820 nm. Accordingly, development of an electrophotographic photosensitive member having high sensitivity to light having such a long wavelength has been advanced.
A phthalocyanine pigment is effective as a charge-generating substance having high sensitivity to light having a wavelength in such a long-wavelength region. In particular, oxytitanium phthalocyanine and a gallium phthalocyanine have excellent sensitivity characteristics, and various crystal forms thereof have been reported heretofore.
An electrophotographic photosensitive member using the gallium phthalocyanine pigment has an excellent sensitivity characteristic. However, the electrophotographic photosensitive member has a drawback in that dispersibility of pigment particles is poor. Consequently, it has been difficult to obtain a coating material for a charge-generating layer excellent in coatability by using such pigment.
As a problem arising when the coatability of the coating material for a charge-generating layer is poor, there can be specifically given a phenomenon in which aggregation of the pigment particles is liable to occur at the time of coating, consequently generating a spot (blue spot) or causing coating unevenness in the charge-generating layer. Particularly when a ratio of the charge-generating substance contained in the charge-generating layer is high, an absolute amount of a resin contained in the charge-generating layer reduces, and hence such problem presents in an additionally remarkable manner. The blue spot in the charge-generating layer causes a black spot or fogging particularly in an output image, while the coating unevenness in the charge-generating layer causes unevenness in image density particularly in a halftone portion. Thus, the blue spot and the coating unevenness cause image quality deterioration.
Japanese Patent Application Laid-Open No. 2005-84350 discloses that a combination of the gallium phthalocyanine and a specific polyvinyl alcohol resin is excellent in coatability and stability of the coating material.
In addition, Japanese Patent Application Laid-Open No. 2001-66804 and Japanese Patent Application Laid-Open No. 2002-229228 disclose that an azotized calixarene compound or a resorcinarene compound is used in the photosensitive layer. Although Japanese Patent Application Laid-Open No. 2001-66804 and Japanese Patent Application Laid-Open No. 2002-229228 disclose that the use of the arene compound alleviates a ghost phenomenon, there are no descriptions of the dispersibility or the coatability thereof.
As described above, various improvements have been attempted for an electrophotographic photosensitive member.
However, a high-quality output image free of any black spot or fogging and free of any density unevenness has been desired in association with an additional improvement in image quality in recent years.